feat: Session Intelligence Layer — /checkpoint + /health + context recovery (v0.15.0.0) (#733)

* feat: session timeline binaries (gstack-timeline-log + gstack-timeline-read)

New binaries for the Session Intelligence Layer. gstack-timeline-log appends
JSONL events to ~/.gstack/projects/$SLUG/timeline.jsonl. gstack-timeline-read
reads, filters, and formats timeline data for /retro consumption.

Timeline is local-only project intelligence, never sent anywhere. Always-on
regardless of telemetry setting.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: preamble context recovery + timeline events + predictive suggestions

Layers 1-3 of the Session Intelligence Layer:
- Timeline start/complete events injected into every skill via preamble
- Context recovery (tier 2+): lists recent CEO plans, checkpoints, reviews
- Cross-session injection: LAST_SESSION and LATEST_CHECKPOINT for branch
- Predictive skill suggestion from recent timeline patterns
- Welcome back message synthesis
- Routing rules for /checkpoint and /health

Timeline writes are NOT gated by telemetry (local project intelligence).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: /checkpoint + /health skills (Layers 4-5)

/checkpoint: save/resume/list working state snapshots. Supports cross-branch
listing for Conductor workspace handoff. Session duration tracking.

/health: code quality scorekeeper. Wraps project tools (tsc, biome, knip,
shellcheck, tests), computes composite 0-10 score, tracks trends over time.
Auto-detects tools or reads from CLAUDE.md ## Health Stack.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* chore: regenerate SKILL.md files + add timeline tests

9 timeline tests (all passing) mirroring learnings.test.ts pattern.
All 34 SKILL.md files regenerated with new preamble (context recovery,
timeline events, routing rules for /checkpoint and /health).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* chore: bump version and changelog (v0.15.0.0)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* docs: update self-learning roadmap post-Session Intelligence

R1-R3 marked shipped with actual versions. R4 becomes Adaptive Ceremony
(trust as separate policy engine, scope-aware, gradual degradation). R5
becomes /autoship (resumable state machine, not linear chain). R6-R7
unbundled from old R5. Added State Systems reference, Risk Register
(Codex-reviewed), and validation metrics for R4.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* test: E2E tests for Session Intelligence (timeline, recovery, checkpoint)

3 gate-tier E2E tests:
- timeline-event-flow: binary data flow round-trip (no LLM)
- context-recovery-artifacts: seeded artifacts appear in preamble
- checkpoint-save-resume: checkpoint file created with YAML frontmatter

Also fixes package.json version sync (0.14.6.0 → 0.15.0.0).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

browse/SKILL.md

@@ -72,6 +72,8 @@ if [ -f "$_LEARN_FILE" ]; then
 else
   echo "LEARNINGS: 0"
 fi
+# Session timeline: record skill start (local-only, never sent anywhere)
+~/.claude/skills/gstack/bin/gstack-timeline-log '{"skill":"browse","event":"started","branch":"'"$_BRANCH"'","session":"'"$_SESSION_ID"'"}' 2>/dev/null &
 # Check if CLAUDE.md has routing rules
 _HAS_ROUTING="no"
 if [ -f CLAUDE.md ] && grep -q "## Skill routing" CLAUDE.md 2>/dev/null; then
@@ -195,6 +197,8 @@ Key routing rules:
 - Design system, brand → invoke design-consultation
 - Visual audit, design polish → invoke design-review
 - Architecture review → invoke plan-eng-review
+- Save progress, checkpoint, resume → invoke checkpoint
+- Code quality, health check → invoke health
 ```
 
 Then commit the change: `git add CLAUDE.md && git commit -m "chore: add gstack skill routing rules to CLAUDE.md"`
@@ -273,6 +277,8 @@ Run this bash:
 _TEL_END=$(date +%s)
 _TEL_DUR=$(( _TEL_END - _TEL_START ))
 rm -f ~/.gstack/analytics/.pending-"$_SESSION_ID" 2>/dev/null || true
+# Session timeline: record skill completion (local-only, never sent anywhere)
+~/.claude/skills/gstack/bin/gstack-timeline-log '{"skill":"SKILL_NAME","event":"completed","branch":"'$(git branch --show-current 2>/dev/null || echo unknown)'","outcome":"OUTCOME","duration_s":"'"$_TEL_DUR"'","session":"'"$_SESSION_ID"'"}' 2>/dev/null || true
 # Local analytics (gated on telemetry setting)
 if [ "$_TEL" != "off" ]; then
 echo '{"skill":"SKILL_NAME","duration_s":"'"$_TEL_DUR"'","outcome":"OUTCOME","browse":"USED_BROWSE","session":"'"$_SESSION_ID"'","ts":"'$(date -u +%Y-%m-%dT%H:%M:%SZ)'"}' >> ~/.gstack/analytics/skill-usage.jsonl 2>/dev/null || true